A six-arm piezoelectric vibratory gyroscope that is capable of detecting angular velocity in a highly accurate manner is disclosed in Japanese Unexamined Patent Application Publication No. 2001-255152. The six-arm piezoelectric vibratory gyroscope includes a piezoelectric body, and drive-side electrodes and detection-side electrodes coupled with the piezoelectric body. The piezoelectric body includes a flat rectangular body having front and back surfaces as main surfaces, a drive-side arm unit extending from one of two opposing sides of the body, and a detection-side arm unit extending from the other side of the body. The drive-side arm unit includes a pair of exciting arms and a non-exciting arm interposed between the exciting arms. The detection-side arm unit includes a pair of detecting arms and a non-detecting arm interposed between the detecting arms. On each of the exciting arms, the drive-side electrodes for exciting in-plane vibration in a direction parallel to the main surfaces of the body are provided. On each of the detecting arms, the detection-side electrodes for detecting plane-perpendicular vibration in a direction perpendicular to the main surfaces of the body are provided. Usually, the exciting arms, the non-exciting arm, the detecting arms, and the non-detecting arm are all produced with the same width and thickness so that they are suitable for mass-production.
To provide a highly sensitive six-arm piezoelectric vibratory gyroscope, the resonant frequency in a driving vibration mode (i.e., in-plane vibration) of each arm of the drive-side arm unit and the resonant frequency in a detection vibration mode (i.e., plane-perpendicular vibration) of each arm of the detection-side arm unit must be similar values. However, in such a case, the plane-perpendicular vibration and the in-plane vibration of each of the six arms become similar to each other. Therefore, spurious frequencies are generated in the vicinities of the driving vibration mode and the detection vibration mode, and the spurious vibration of the in-plane vibration is excited so as to mechanically couple the arms to a piezoelectric transducer or a piezoelectric body. As a result, the gyro sensitivity, i.e., the detection sensitivity, is significantly reduced. In particular, since the intensity of the spurious vibration of the in-plane vibration is significantly greater than the intensity of the spurious vibration of the plane-perpendicular vibration, the gyro sensitivity is reduced.